It is well established that surgical patients under anesthesia become poikilothermic. This means that the patients lose their ability to control their body temperature and will take on or lose heat depending on the temperature of the environment. Since modern operating rooms are all air conditioned to a relatively low temperature for caregiver comfort, the majority of patients undergoing general anesthesia will lose heat and become clinically hypothermic if not warmed.
Over the past 15 years, forced-air warming (FAW) has become the “standard of care” for preventing and treating the hypothermia caused by anesthesia and surgery. FAW consists of a large heater/blower attached by a hose to an inflatable air blanket. The warm air is distributed over the patient within the chambers of the blanket and then is exhausted onto the patient through holes in the bottom surface of the blanket.
Although FAW is clinically effective, it suffers from several problems including: a relatively high price; air blowing in the operating room, which can be noisy and can potentially contaminate the surgical field; and bulkiness, which, at times, may obscure the view of the caregiver (e.g., surgeon, physician, nurse, etc.). Moreover, the low specific heat of air and the rapid loss of heat from air require that the temperature of the air, as it leaves the hose, be dangerously high—in some products as high as 45° C. This poses significant dangers for the patient. Second and third degree burns have occurred both because of contact between the hose and the patient's skin, and by blowing hot air directly from the hose onto the skin without connecting a blanket to the hose. This condition is common enough to have its own name—“hosing.” The manufacturers of forced air warming equipment actively warn their users against hosing and the risks it poses to the patient.
To overcome the aforementioned problems with FAW, several companies have developed electric warming blankets. However, these electric blankets have a number of inadequacies, such as the risk of heat and pressure injuries that may be suffered by a patient improperly coming into contact with the electrical heating elements of these blankets. It is well established that heat and pressure applied to the skin can rapidly cause thermal injury to that skin. Such contact may arise if a patient inadvertently lies on an edge of a heated blanket, if a clinician improperly positions an anesthetized patient atop a portion of the heated blanket, or if a clinician tucks an edge of the blanket about the patient. Thus, there is a need for a heating blanket that effectively forms a cocoon about a patient, in order to provide maximum efficacy in heating, without posing the risk of burning the patient.
There is also a need for electrically heated blankets or pads that can be used safely and effectively to warm patients undergoing surgery or other medical treatments. These blankets need to be flexible in order to effectively drape over the patient (making excellent contact for conductive heat transfer and maximizing the area of the patient's skin receiving conductive as well as radiant heat transfer), and should incorporate means for precise temperature control.
In some instances, patient-warming blankets that take the form of traditional blankets can be less than ideally suited. For example, in some instances, a patient's chest, abdomen, and legs must both be exposed, making traditionally formed blankets a less attractive option. In some cardiac surgical procedures, for example, patients are “prepped” (e.g., scrubbed and sterilized) from their neck to their feet, except for their arms. In such procedures, the sterile surgical field includes the front (anterior) chest, abdomen, groin and legs, leaving minimal exposed skin to which surface warming can be applied. Additionally, heating a patient's back in such instances, which is supporting his or her weight, can be dangerous, as mentioned above, because applying heat to areas that are also subject to pressure due to weight bearing, can cause full thickness skin damage or necrosis. Like such cardiac surgical procedures, abdominal or leg operations in which patients' arms are tucked at their sides can leave minimal skin surface to which surface warming can be applied.
Similarly, patient-warming blankets that take the form of traditional blankets can be less than ideally suited in an emergency room environment. Emergency room physicians often want as much of the patient exposed as possible for easy and ongoing examinations and monitoring, making patient warming via traditionally formed blankets less attractive.